A friend of Mr John­son told The Mail on Sun­day: ‘The divorce pro­ceed­ings ac­tu­ally be­gan in Septem­ber. Boris and Car­rie are in a se­ri­ous re­la­tion­ship.’

The friend added that de­spite the huge in­ter­est in their love life from friends and po­lit­i­cal ri­vals, the cou­ple were try­ing to stay tight-lipped over their re­la­tion­ship. How­ever, it emerged last week that the cou­ple en­joyed a ro­man­tic break over the New Year in a villa on Greece’s Pe­lion penin­sula.

They were recog­nised by ex­pat Chris Wicks as they dined out in a tav­erna in Lafkos.

Mr John­son is said to be so in love that he be­haves ‘like a puppy dog around her’.

A friend said: ‘He wants to get en­gaged. He’s com­pletely in thrall to Car­rie. To­tally loved-up.’

It emerged in Septem­ber that Boris and his wife Ma­rina were plan­ning to divorce af­ter 25 years of mar­riage. It came amid re­ports that fa­ther- of- four Mr John­son had be­gun a re­la­tion­ship with Ms Sy­monds, a for­mer Tory Party com­mu­ni­ca­tions chief who is now an ad­viser to fi­nan­cial firm Bloomberg.

An­other ally of Mr John­son was quoted yes­ter­day as say­ing Ms Sy­monds seems to makes him ‘very happy’. The friend added: ‘Car­rie has been the per­fect girl­friend. He and Ma­rina split in March, so it shouldn’t be a sur­prise that this re­la­tion­ship is se­ri­ous by now.’ The friend said the cou­ple had been try­ing to ‘keep things dis­creet’, adding: ‘No­body wants to see Ma­rina hu­mil­i­ated by pub­lic dis­plays.’

It is un­der­stood Ms Sy­monds has yet to meet Mr John­son’s chil­dren.

In Septem­ber when they an­nounced they were to divorce, Mr John­son and his wife stressed that ‘as friends, we will con­tinue to sup­port our four chil­dren in the years ahead’.

The cou­ple had been liv­ing at his £20 mil­lion grace-and-favour home in Carl­ton Gar­dens, the of­fi­cial res­i­dence of the For­eign Sec­re­tary, un­til the end of July.

They own a £4 mil­lion town­house in Is­ling­ton as well as a coun­try home in Ox­ford­shire. Boris mar­ried first wife Al­le­gra Mostyn- Owen in 1987. He mar­ried Ma­rina, a QC, in 1993. But a string of af­fairs fol­lowed and Ma­rina kicked him out twice, only to take him back.

The first t i me was i n 2004 over his af­fair with writer Petronella Wy­att.

The sec­ond came six years later, when he was sus­pected of hav­ing a love- child with art con­sul­tant He­len Mac­in­tyre.